Lens unit and manufacturing method of lens unit

ABSTRACT

A lens unit includes a positive lens element provided with a convex surface on an incident surface and/or an exit surface; and a lens frame supporting the lens element and being provided with a projection that projects in an inner radial direction from inside the lens frame. The lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element. The projection is provided, on an inner peripheral portion thereof, with a first surface positioned on an incident side in an optical axis direction, a second surface positioned on an exit side in the optical axis direction, and a third surface positioned between the first surface and the second surface. The first, second and third surfaces are tapered surfaces that are respectively inclined relative to the optical axis direction. A method of manufacturing the lens unit is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No. 16/725,284, filed Dec. 23, 2019, which claims the benefit of Japanese Patent Application No. 2018-247242, filed Dec. 28, 2018. The disclosure of each of these documents, including the specification, drawings, and claims, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a lens unit and a manufacturing method thereof.

2. Description of Related Art

In an optical instrument such as an optical communication device or projector, etc., a lens unit, in which a lens element (or lens group) is fixedly supported inside a tubular lens frame, is used at a location to which light is distributed from a light source. The lens unit is mounted at a predetermined position relative to the light source, and light emitted (divergent light) from the light source condenses (focuses) at a predetermined position via the lens element of the lens unit.

In such a type of lens unit, it is demanded that the lens element be firmly supported inside the lens frame with high precision. Furthermore, if the space between the light source and the lens element is filled with an inert gas, or the like, there is also a demand for airtightness to be maintained between the lens element and the lens frame. In order to meet such demands, a structure having increased lens-element support (retention) is known in which a projection formed on an inner periphery of the lens frame fit-engages with an outer periphery of the lens element.

Furthermore, in a lens unit, only light distribution of effective light rays that properly pass within the effective apertures of the incident surface and exit surface of the lens element are desired. Whereas, since light other than effective light rays, such as peripheral light, reflection light and stray light, etc., become a cause of ghosting, etc., various techniques have been proposed in order to shield (shut out) such harmful light using part of the lens frame.

The above-mentioned related arts are disclosed in the following documents.

Patent Literature 1: Japanese Unexamined Patent Publication No. 2010-156905

Patent Literature 2: Japanese Unexamined Patent Publication No. 2001-350075

Patent Literature 3: Japanese Patent No. 2,729,702

Patent Literature 4: International Patent Publication No. WO2016-051619

The demand for further miniaturization and improvement in optical performance of lens units has increased in recent years. Specifically, improvements in positional precision and joining strength between the lens frame and the lens element are demanded, as well as the demand for suppression of harmful light rays. Furthermore, improvement in manufacturability of lens units is also demanded.

SUMMARY OF THE INVENTION

In view of the aforementioned problems, the illustrated embodiment of the invention provides a lens unit that possesses superior positional precision and joining strength between a lens frame and a lens element. The illustrated embodiment of the invention also provides a lens unit possessing superior optical performance in which harmful light rays are prevented. A manufacturing method of a lens unit is also disclosed which is superior in manufacturability.

According to an embodiment of the invention, a lens unit including a lens element provided with a convex surface on at least one of an incident surface and an exit surface of the lens element, the lens element having a positive refractive power that condenses light rays, emitting from a light source, at a predetermined position; and a lens frame that supports the lens element within the lens frame, the lens frame provided with a projection that projects in an inner radial direction from an inner portion of the lens frame. The lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element. The projection is provided, on an inner peripheral portion thereof, with a first surface positioned on an incident side in an optical axis direction of the lens element, a second surface positioned on an exit side in the optical axis direction, and a third surface positioned between the first surface and the second surface. The first, second and third surfaces are tapered surfaces that are respectively inclined relative to the optical axis direction.

According to the above-described embodiment of the lens unit, since the projection in the lens frame is provided with first through third surfaces that incline relative to the optical axis direction, the precision and strength of support (retention) of the lens element that is supported (held/retained) by the projection can be improved. Furthermore, the projection in the lens frame shields light that passes outside the effective aperture diameter of the lens element, thereby improving optical performance.

By appropriately determining the orientation and shape of the tapered surfaces that define the projection in the lens frame, the optical performance can be further improved. For example, it is desirable to determine the relative position and shape of the exit surface and the third surface so that light rays that are incident from the incident surface and reflect off the third surface are totally reflected by the exit surface. Accordingly, the projection does not just merely shield unwanted and harmful peripheral light, but also prevents light that is reflected off the projection itself from exiting the lens element.

It is desirable for the third surface of the projection to have a progressively reduced inner diameter toward a surface having a largest convex curvature out of the incident surface and the exit surface.

In the projection in the lens frame, the first surface may have a progressively reduced inner diameter from the incident side to the exit side, the second surface may have a progressively reduced inner diameter from the exit side to the incident side, and the third surface may have a progressively reduced inner diameter from the incident side to the exit side. An inclination of the third surface relative to the optical axis direction can be different from that of the first surface. Alternatively, it is also possible for the third surface to have a progressively reduced inner diameter from the exit side to the incident side, and for an inclination of the third surface relative to the optical axis direction to ire different from that of the second surface.

The lens frame may be provided, on an inner surface thereof, with a ref lection control portion between the source and the lens element with respect to the optical axis direction, wherein light rays from the light source are reflected by the reflection control portion and travel toward the projection. Accordingly, reflected light rays that reflect from the inner surface of the lens frame before entering the lens element can also be effectively shielded (shut out), to thereby further improve the optical performance of the lens unit.

It is desirable, as a method of manufacturing the above-described lens unit, to place the lens frame into a press-molding apparatus with the lens frame oriented so that an end of the third surface that has a smaller inner diameter than the other end, with respect to the optical axis direction, is positioned downward; to place a glass preform onto the third surface; and to press-mold the glass preform using an upper die and a lower die of the press-molding apparatus to form the lens element. Since the glass preform can be supported by the third surface, which has a progressively reduced diameter in a downward direction, before the glass preform is molded (press-molded) the relative position between the glass preform and the lens frame can be determined with high precision from a preparatory stage of a pressing operation and during the pressing operation itself.

In the method of manufacturing the above-described lens unit, it is desirable for a molding surface for molding one surface having a largest convex curvature out of the incident surface and the exit surface of the lens element to be formed on the lower die, and a molding surface for molding the other surface of the incident surface and the exit surface of the lens element to be formed on the upper die. By providing the molding surface, for molding the surface of the lens that has a larger convex curvature, in the lower die (lower mold), positional precision and stability of the glass preform during the press-molding operation using the upper and lower dies can be improved.

As described above, according to the lens unit of the present disclosure, the positional precision and joining strength between the lens frame and the lens element can be improved. Furthermore, according to the lens unit of the present disclosure, optical performance is improved by using a simple structure to prevent harmful light rays from passing through the lens element.

Furthermore, according to the present disclosure of the method of manufacturing the lens unit, productivity of the lens unit which supports (holds) a lens element within a lens frame can be improved.

The present disclosure relates to subject matter contained in Japanese Patent Application No. 2018-247242 (filed on Dec. 28, 2018) which is expressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of an optical device provided with a lens unit according to a first embodiment;

FIG. 2 is a cross-sectional perspective view taken along the optical axis of the optical device that is provided with the lens unit according to the first embodiment;

FIG. 3 is a cross-sectional view of main components of an optical device that is provided with the lens unit according to the first embodiment;

FIG. 4 is a cross-sectional view, of the lens unit according to the first embodiment, illustrating effective light rays in the lens unit;

FIG. 5 is a cross-sectional view, of the lens unit according to the first embodiment, illustrating the shielding of peripheral light rays by the lens unit;

FIG. 6 is an enlarged sectional view of part of FIG. 5;

FIG. 7 is a cross-sectional view of the lens unit according to the first embodiment illustrating light rays that are reflected by a projection on the lens frame being totally reflected off the exit surface of the lens element;

FIG. 8 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a first comparative embodiment;

FIG. 9 is a cross-sectional view illustrating a state in which light rays pass through the lens unit according to the first comparative embodiment;

FIG. 10 is a cross-sectional view illustrating a state in which light rays are reflected from an inner surface of a lens frame of the lens unit according to the first comparative embodiment;

FIG. 11 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a second comparative embodiment;

FIG. 12 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a third comparative embodiment;

FIG. 13 is a cross-sectional view of a press-molding ready state for a lens element in a molding apparatus for manufacturing the lens unit according to the first embodiment;

FIG. 14 is a cross-sectional view of partway through a press-molding operation on a lens element in the molding apparatus for manufacturing the lens unit according to the first embodiment;

FIG. 15 is a cross-sectional view of a press-molding completion state of a lens element in the molding apparatus for manufacturing the lens unit according to the first embodiment;

FIG. 16 is an enlarged cross-sectional view of part of FIG. 13 ;

FIG. 17 is an enlarged cross-sectional view of part of FIG. 14 ;

FIG. 18 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a second embodiment;

FIG. 19 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a third embodiment;

FIG. 20 is a cross-sectional view of a press-molding ready state for a lens element in a molding apparatus for manufacturing the lens unit according to the third embodiment;

FIG. 21 is a cross-sectional view of a press-molding completion state of a lens element in the molding apparatus for manufacturing the lens unit according to the third embodiment;

FIG. 22 is a cross-sectional view of main components of an optical device that is provided with a lens unit according to a fourth embodiment;

FIG. 23 is a cross-sectional view of a press-molding ready state for a lens element in a molding apparatus for manufacturing the lens unit according to the fourth embodiment; and

FIG. 24 is a cross-sectional view of a press-molding completion state of a lens element in the molding apparatus for manufacturing the lens unit according to the fourth embodiment.

DESCRIPTION OF THE EMBODIMENTS

A lens unit 2 according to a first embodiment will be hereinafter discussed with reference to FIGS. 1 through 7 . The lens unit 2 is combined with a light source unit 3 to form an optical device 1. The optical device 1 is used in a light distribution portion of an optical instrument such as a projector, an optical information-reading apparatus, or an optical communication apparatus, etc.

The lens unit 2 is formed from a lens element 10 and a lens frame 20. The lens element 10 has a positive refractive power and constitutes (at least part of) a converging optical system (condensing optical system/focusing optical system) which converges light, emitted from a light source 30 of the light source unit 3, at a predetermined position (a point of focus).

The lens element 10 is a single lens element made from a glass material. The lens element 10 has a profile (shape) that is rotationally symmetrical about optical axis 10 x. Hereinafter, a direction that extends along the optical axis 10 x will be referred to as an “optical axis direction”. With respect to the optical axis direction, an “incident side” is defined as facing toward the light source 30 in the optical axis direction, and an “exit side” is defined as facing away from (in an opposite direction from) the light source 30 in the optical axis direction. Furthermore, with respect to a radial direction about the optical axis 10 x, a radial direction toward the optical axis 10 x will be herein referred to as an “inner radial direction” and a radial direction extending an opposite direction away from the optical axis 10 x will be herein referred to as an “outer radial direction”.

The lens element 10 is provided with an incident surface 11 on the incident side thereof, and with an exit surface 12 on the exit side thereof. The incident surface 11 is a flat surface orthogonal to the optical axis 10 x. The exit surface 12 is a convex surface convexing toward (protruding toward) the exit side. In other words, the lens element 10 is a plano-convex lens. An exit peripheral rim surface 13 is formed at a peripheral annular region of the exit surface 12. The exit peripheral rim surface 13 is approximately perpendicular (orthogonal) to the optical axis 10 x.

With respect to the lens element 10, the areas through which effective light rays EL shown in FIG. 5 pass define an effective aperture on the incident side and an effective aperture on the exit side, respectively. The effective aperture on the exit side lies within the range defined (formed) by the exit surface 12. The exit peripheral rim surface 13 is a portion needed for when the lens element 10 is formed (molded), which is discussed further below. The exit peripheral rim surface 13 does not function as an effective lens surface. The effective aperture of the exit surface 12 is larger than the effective aperture of the incident surface 11.

A radially-outer peripheral part of the lens element 10 is provided with an outer peripheral recess (outer peripheral depression) 14 having a shape that is recessed in the inner radial direction. When the lens element 10 is formed (press-molded), which is discussed further below, the outer peripheral recess 14 is formed by a projection 26 (the details of which will be discussed below), which constitutes part of the lens frame 20.

The lens frame 20 is a metal tubular body having a central axis extending in the optical axis direction. The lens frame 20 is provided with an incident end 21 at the incident side (with respect to the lens element 10), and an exit end 22 at the exit side (with respect to the lens element 10). Both of the incident end 21 and the exit end 22 are flat surfaces lying orthogonal to the optical axis 10 x. A through-hole 23 is formed through the lens frame 20 and extends from the incident end 21 through to the exit end 22 in the optical axis direction.

The outer peripheral surface of the lens frame 20 has a smooth cylindrical shape; however, due to differences in the inner peripheral shape (profile) of the through-hole 23, the lens frame 20 is divided (defined) by three sections with respect to the optical axis direction. Specifically, as shown in FIG. 3 , the lens frame 20 is defined by an incident-side section 20A that is located towards the incident end 21, an exit-side section 20B that is located towards the exit end 22, and an intermediate section 20C that is located between the incident-side section 20A and the exit-side section 20B.

An inner surface of the incident-side section 20A that defines part of the through-hole 23 (within the incident-side section 20A) is formed as a cylindrical surface 24 (inner cylindrical surface) having a uniform profile (constant diameter) along the optical axis direction. The inner diameter of the cylindrical surface 24 is slightly larger than the outer diameter of the incident surface 11 of the lens element 10.

An inner surface of the exit-side section 20B that defines another part of the through-hole 23 (within the exit-side section 20B) is formed as a cylindrical surface 25 (inner cylindrical surface) having a uniform profile (constant diameter) along the optical axis direction. The inner diameter of the cylindrical surface 25 is slightly larger than the outer diameter of the exit peripheral rim surface 13 of the lens element 10.

The intermediate section 20C is provided with the projection 26, which projects in an inner radial direction relative to the cylindrical surface 24 and the cylindrical surface 25. The projection 26 is continuously provided (without discontinuing) around the entire inner circumference of the lens frame 20 and has a cross-sectional shape, as shown in FIGS. 2 through 7 , at all positions in the circumferential direction. The projection 26 is provided with a first tapered surface (first surface) 26 a that connects with the exit end of the cylindrical surface 24, a second tapered surface (second surface) 26 b that connects with the incident end of the cylindrical surface 25, and a third tapered surface (third surface) 26 c connected between the first tapered surface 26 a and the second tapered surface 26 b.

Each of the first tapered surface 26 a, the second tapered surface 26 b, and the third tapered surface 26 c has a conic shape (defining part of a conic surface) centered about the optical axis 10 x. The first tapered surface 26 a has a progressively reduced inner diameter from the cylindrical surface 24 (the incident side) toward the exit side. The second tapered surface 26 b has a progressively reduced inner diameter from the cylindrical surface 25 (exit side) toward the incident side. The third tapered surface 26 c has a progressively reduced inner diameter from the first tapered surface 26 a (incident side) toward the second tapered surface 26 b (exit side). In other words, the first tapered surface 26 a and the third tapered surface 26 c are tapered surfaces that have a gradually decreasing inner diameter toward the exit side, and the second tapered surface 26 b is a tapered surface that has a gradually decreasing inner diameter toward the incident side.

The inclination angle of the first tapered surface 26 a relative to the optical axis 10 x is greater than that of the third tapered surface 26 c. In addition, ignoring the fact that the inclination directions are opposite to each other, the inclination angle of the second tapered surface 26 b relative to the optical axis 10 x is greater than that of the first tapered surface 26 a. In terms of ranges occupied in the optical axis direction, as shown in FIG. 3 , a range K2 in which the second tapered surface 26 b is formed is the narrowest, a range K3 in which the third tapered surface 26 c is formed is the widest, and a range K1 in which the first tapered surface 26 a is formed has an intermediate width. A maximum projecting portion (maximum projecting point) 26 d, which projects the most in the inner radial direction out of (all other positions in the optical axis direction of) the projection 26, is positioned at a boundary defined between the second tapered surface 26 b and the third tapered surface 26 c. The position of the maximum projecting portion 26 d is located toward the exit side relative to a central position in the optical axis direction of the intermediate section 20C.

The lens element 10 is accommodated within the through-hole 23 and integrally formed with the lens frame 20 with the projection 26 fixedly fitted into the outer peripheral recess 14. The outer peripheral recess 14 has an inner surface shape including three tapered surfaces that respectively correspond to the three tapered surfaces 26 a, 26 b and 26 c that form (define) the projection 26. Accordingly, the projection 26 fit-engages with the outer peripheral recess 14 to thereby integrally connect the lens element 10 and the lens frame 20 with each other. This type of joining structure (mated structure) is achieved by forming the lens element 10 while being embedded in the lens frame 20.

The exit peripheral rim surface 13 of the lens element 10 is positioned near or at a boundary between the exit-side section 20B and the intermediate section 20C with respect to the optical axis direction. The length in the optical axis direction of the exit-side section 20B of the lens frame 20 is set to a larger length than the protruding amount (convexing amount) of the exit surface 12 from the exit peripheral rim surface 13 of the lens element 10. In other words, the exit end 22 of the lens frame 20 is positioned further toward the exit side than the exit surface 12 of the lens element 10. Furthermore, the incident surface 11 of the lens element 10 is positioned near, or at, a boundary between the incident-side section 20A and the intermediate section 20C with respect to the optical axis direction. Accordingly, the entire lens element 10 is accommodated within the through-hole 23 in the optical axis direction. The incident-side section 20A of the lens frame 20 functions as a spacer that determines (defines) a distance in the optical axis between the incident surface 11 of the lens element 10 and the light source 30.

The light source unit 3 is provided with an internal body 31 that accommodates the light source 30 therein. An aperture portion 32 is formed in the internal body 31, and an inner side of the aperture portion 32 is covered with a transparent cover glass 33. An outer body 34, having a larger diameter than that of the lens frame 20, is provided on the outer side of the internal body 31. The internal body 31 is fixedly fitted into an accommodation portion 35 that is formed in the outer body 34.

The outer body 34 is provided with a conical shaped light-source peripheral-edge surface 36 which has a gradually increasing aperture diameter from the accommodation portion 35 toward the outer surface. The lens unit 2 and the light source unit 3 are assembled together by abutting the incident end 21 of the lens frame 20 against the outer body 34 at the outer periphery of the light-source peripheral-edge surface 36. The lens unit 2 and the light source unit 3 are aligned and mutually fixed so that a predetermined positional relationship is obtained between the lens element 10 and the light source 30. In a state where the lens unit 2 and the light source unit 3 assembled together and mutually fixed, the inside (the internal space at the incident side of the lens element 10) of the lens frame 20 is filled with inert gas.

In the lens unit 2, the structure that holds the lens element 10 by the three tapered surfaces 26 a, 26 b and 26 c of the projection 26 of the lens frame 20 corning in contact with the lens element 10 is superior in joining strength, positional precision, load bearing and air-tightness. Since each of the three tapered surfaces 26 a, 26 b and 26 c is non-parallel and non-orthogonal relative to the optical axis 10 x, each of the three tapered surfaces 26 a, 26 b and 26 c can function as a positional reference for both the optical axis direction and the radial direction, and can receive loads acting in both the optical axis direction and the radial direction. Furthermore, due to the tapered surfaces 26 a, 26 b and 26 c constituting complex tapered surfaces having mutually different inclination angles and being in contact with the lens element 10, the air-tightness between the projection 26 and the outer peripheral recess 14 is improved (increased). In particular, in addition to the first tapered surface 26 a and the second tapered surface 26 b that form the projection profile of the projection 26, adjacent to the cylindrical surfaces 24 and 25, the third tapered surface 26 c that is positioned between the first and second tapered surfaces 26 a and 26 b also can achieve the above-described advantageous effects over the entire projection 26 by being inclined relative to the optical axis 10 x.

The optical device 1 is constructed in the above-described manner. Light emitted from the light source 30 is diverged and travels toward the lens element 10, and is converged (focused) at a predetermined converging position by the positive refractive power of the lens element 10. Light rays travelling from light-emission point LP of the light source 30 are schematically shown in FIGS. 4 through 7 . Out of the light rays that originate from the light-emission point LP, the effective light rays EL that pass within the effective apertures of the incident surface 11 and the exit surface 12 without being reflected, etc., by the lens frame 20 are shown in FIGS. 4 through 6 . Out of the effective light rays EL, the light rays that pass through both the incident surface 11 and the exit surface 12 at a maximum position away from the optical axis 10 x are referred to as outermost effective light rays ELz. The distances in the radial direction from the optical axis 10 x to the outermost effective light rays ELz at the incident surface 11 and at the exit surface 12 respectively define the effective apertures thereof.

As shown in FIGS. 4 through 6 , the outermost effective light rays ELz pass at a close proximity of the maximum projecting portion 26 d that projects by a maximum amount in the inward radial direction of the lens frame 20. The projection 26 does not obstruct the outermost effective light rays ELz and functions as a light shield that shields light that passes on the outer radial side of the outermost effective light rays ELz travelling toward the exit side.

Peripheral light rays OL which are incident on the lens element 10 from the outer side of the effective aperture of the incident surface 11 and pass on the outer radial side of the outermost effective light rays ELz of the effective light rays EL are shown in FIGS. 5 and 6 . The peripheral light rays OL are obstructed by the projection 26 so that the peripheral light rays OL cannot travel any further therefrom and not exit from the lens element 10. For example, peripheral light ray OL1 shown in FIG. 6 is a light ray that is incident outside the effective aperture of the incident surface 11 and heads toward a boundary portion between the exit surface 12 and the exit peripheral rim surface 13. Peripheral light ray OL2 is a light ray that is incident outside the effective aperture of the incident surface 11 and heads toward the exit peripheral rim surface 13. Peripheral light ray OL3 is a light ray that is incident outside the effective aperture of the incident surface 11 and heads toward an outermost peripheral portion of the exit peripheral rim surface 13. The third tapered surface 26 c of the projection 26 is positioned on extension lines of the peripheral light rays OL1, OL2 and OL3 so that further travel of each of the peripheral light rays OL1, OL2 and OL3 is obstructed (prevented) by the third tapered surface 26 c of the projection 26. Furthermore, the first tapered surface 26 a of the projection 26 is positioned on an extension line of peripheral light ray OL4 that is incident outside the effective aperture of the incident surface 11 and heads toward a position radially outside the exit peripheral rim surface 13, so that further travel of the peripheral light ray OL4 is obstructed (prevented) by the first tapered surface 26 a of the projection 26.

Accordingly, the projection 26 provided in the lens frame 20 is positioned on the travelling path (light path) of the peripheral light rays OL, which try to travel along a radially outer side of the exit surface 12, so that the projection 26 obstructs (shields) the peripheral light rays OL. In the projection 26, the maximum projecting portion 26 d is determined (defined) at a boundary between the second tapered surface 26 b and the third tapered surface 26 c, which respectively incline relative to the optical axis 10 x, and light rays that are allowed to pass through the lens element 10 (outermost effective light rays ELz) and light rays that are shielded (peripheral light rays OL) are managed (determined) by the position of the maximum projecting portion 26 d. By determining the light-shielding boundary at a specified point such as at the maximum projecting portion 26 d, precise management of the shielding effect attained by the projection 26 is facilitated, and light shielding can be achieved at a high precision.

The lens unit 2 is also provided with a function of preventing reflection light that is reflected from the projection 26 (which holds the lens element 10) and heads toward the exit surface 12 from becoming harmful light. FIG. 7 indicates a reflection light ray RL1 and a reflection light ray RL2 which each enter from (made incident on) the incident surface 11, are each reflected by the third tapered surface 26 c of the projection 26 and travel toward the exit surface 12. The third tapered surface 26 c is formed to satisfy conditions so that each of the reflection light rays RL1 and RL2 totally reflect at the exit surface 12 (i.e., so total internal reflection (TIR) of the reflection light rays RL1 and RL2 respectively occurs at the exit surface 12).

Specifically, the angle of the third tapered surface 26 c is determined so that incident angle α of the reflection light ray RL1 relative to the exit surface 12 and the incident angle β of the reflection light ray RL2 relative to the exit surface 12 are each greater than the critical angle for total internal reflection. Accordingly, at the exit surface 12, which defines a boundary between the lens element 10 (a medium having a relatively large refractive index) and air (a medium having a relatively small refractive index), the refractive angles of the reflection light ray RL1 and the reflection light ray RL2 each become greater than 90 degrees, so that total internal reflection of each of these light rays occurs. Note that although FIG. 7 shows specific reflection light rays RL1 and RL2, all light rays that originate from the light-emission point LP and reach the third tapered surface 26 c via only refraction at the incident surface 11 satisfy the total internal reflection conditions at the boundary between the exit surface 12 and air. In the projection 26, the first tapered surface 26 a that is positioned on the incident side relative to the third tapered surface 26 c is inclined relative to the optical axis 10 x by a larger angle than that of the third tapered surface 26 c, and light rays that are reflected from the first tapered surface 26 a do not travel toward the exit surface 12. Whereas, the second tapered surface 26 b, which is positioned on the exit side of the third tapered surface 26 c, is a surface that has a progressively greater inner diameter in a direction toward the exit side (a surface that is inclined in a direction opposite to that of the third tapered surface 26 c), and all light rays (originating from the light source 30) that pass through the incident surface 11 and travel toward the projection 26 are either shielded or reflected by the first tapered surface 26 a or the third tapered surface 26 c and do not directly reach (arrive at) the second tapered surface 26 b. Accordingly, if the profile (shape and angle) of the third tapered surface 26 c is determined so that the above-mentioned total internal reflection conditions are satisfied, an advantageous effect of being able to prevent harmful light by the entire projection 26, which is in contact with the outer peripheral recess 14 of the lens element 10, can be achieved.

Hence, in the lens unit 2, effective light rays EL can be reliably transmitted therethrough while harmful light such as light other than the effective light rays EL (peripheral light rays OL, reflection light rays RL1 and RL2, etc.) can be prevented from passing through the exit surface 12 and exiting therefrom. In particular, harmful light rays can be effectively shielded by the projection 26, which projects in an inward radial direction of the lens frame 20. Furthermore, by determining the inclination angle of the third tapered surface 26 c so that light rays that are reflected by the third tapered surface 26 c and are totally internally reflected at the exit surface 12 so that these light rays do not exit from the exit surface 12, a deterioration in optical performance due to reflection of light rays at an outer peripheral portion of the lens element 10 (at a position where the outer peripheral recess 14 and the projection 26 come in contact) can be appropriately prevented. Accordingly, light can be prevented from diffusing, which causes ghosting to occur, outside an optically designed predetermined range at the light-converging position of the lens element 10, and an improved optical performance of the optical device 1 can be achieved.

Since the projection 26 possesses the above-described light-shielding function in addition to projecting radially inward in the lens frame 20 to hold the lens element 10, there is no need to provide a separate structure dedicated to light shielding, so that the lens unit 2 can have an increased functionally while still having a simple structure. Furthermore, the projection 26 which is formed by a combination of the tapered surfaces 26 a, 26 b and 26 c can be easily manufactured. More specifically, the first tapered surface 26 a and the third tapered surface 26 c each have a profile that is easy to mold or machine (cut) from the incident side of the lens frame 20, and the second tapered surface 26 b has a profile that is easy to mold or machine (cut) from the exit side of the lens frame 20.

Comparative examples which differ from the above-described first embodiment will be hereinbelow described with reference to FIGS. 8 through 12 . In each comparative example, any components that are same in structure with the first embodiment will have the same reference numerals and duplicate descriptions thereof are omitted.

In a first comparative example shown in FIGS. 8 through 10 , in the lens frame 20 that constitutes a major part of the lens unit 2, an inner surface profile of an intermediate section 20C differs from that of the projection 26 of the first embodiment. The inner surface of the intermediate section 20C in the first comparative example is provided with a projection 90, which slightly projects in the inner radial direction relative to the cylindrical surface 24 of the incident-side section 20A and relative to the cylindrical surface 25 of the exit-side section 20B. The projection amount of the projection 90 in the inner radial direction is much smaller than the projection amount of the above-described projection 26 of the first embodiment. An outer peripheral recess 91 having a shape that the projection 90 fits into is formed on the outer periphery of the lens element 10.

More specifically, the projection 90 is provided with a first tapered surface 90 a positioned on the incident side, a second tapered surface 90 b positioned on the exit side, and a connect ion surface 90 c that is connected between the first tapered surface 90 a and the second tapered surface 90 b. The first tapered surface 90 a is a partial conical surface having a progressively reduced diameter from the incident side toward the exit side. The second tapered surface 90 b is a partial conical surface having a progressively reduced diameter from the exit side toward the incident side. The first tapered surface 90 a and the second tapered surface 90 b each have a smaller projection amount in the inner radial direction than that of each of the first tapered surface 26 a and the second tapered surface 26 b of the first embodiment. The connection surface 90 c is a cylindrical surface having a constant diameter extending along the optical axis direction. The part of the projection 90 that is positioned at the innermost radial position is the connection surface 90 c. However, the connection surface 90 c is located at an outer radial position compared to the radial position of the third tapered surface 26 c of the projection 26 of the first embodiment.

As shown in FIG. 9 , the projection 90 only has a small projection amount in the inner radial direction, and moreover, the connection surface 90 c is not inclined relative to the optical axis 10 x. Accordingly, the projection 90 does not shield peripheral light rays OL′ that pass along an outer radial side of the effective light rays EL, so that the peripheral light rays OL′ end up reaching the boundary position between the exit surface 12 and the exit peripheral rim surface 13 of the lens element 10 and/or the position of the exit peripheral rim surface 13. Furthermore, as shown in FIG. 10 , a reflection light ray RL1′ passing through the exit peripheral rim surface 13 and reflecting off the cylindrical surface 25 of the lens frame 20 may occur, a reflection light ray RL2′ that reflects off the cylindrical surface 25 and passes through the exit peripheral rim surface 13 may occur, and reflection light rays RL3′ and RL4′ that reflect off the projection 90 and exit from the lens element 10 (the exit peripheral rim surface 13 or the exit surface 12) may occur. Such peripheral light and reflection light become the cause of ghosting.

Furthermore, since the connection surface 90 c of the projection 90 is a surface that is parallel to the optical axis 10 x, the connection surface 90 c cannot receive a load in the optical axis direction, and the connection surface 90 c cannot be used as a reference position with respect to the optical axis direction.

In a second comparative example shown in FIG. 11 , in addition to the structure of the first comparative example, a diaphragm 92 is provided between the light source 30 and the lens element 10. The diaphragm 92 is provided to cover the light-source peripheral-edge surface 36 of the outer body 34 in the light source unit 3. The diaphragm 92 has a round through-hole 92 a formed therethrough at a central portion of the diaphragm 92. The through-hole 92 a is set to a size that only allows the effective light rays EL to pass through. Light that travels outside (outer radial side of) the effective light rays EL are shielded (shut out) by a plate surface of the diaphragm 92 around the peripheral area of the through-hole 92 a. Therefore, harmful peripheral light does not reach the lens element 10, ghosting can be prevented even though the projection amount of the projection 90 provided on the inner side of the intermediate section 20C is small.

However, since the second comparative example uses the diaphragm 92, which is a light-shielding member that is independent from the lens frame 20, this incurs an increase in the number of components and an increase in manufacturing cost. Furthermore, since the diaphragm 92 is a separate member from the lens frame 20, it is necessary to carry out an adjustment of the positional setting of the diaphragm 92 relative to the lens unit 2 and the light source unit 3 so that only harmful light rays are shielded and not the effective light rays EL, thereby causing the precision management and manufacture to become complicated.

In a third comparative example shown in FIG. 12 , a projection 93, which is formed on an inner surface of the intermediate section 20C of the lens frame 20, has a different shape to that of the projection 26 of the first embodiment. More specifically, the projection 93 is provided with a first tapered surface 93 a that connects with the exit end of the cylindrical surface 24, a second tapered surface 93 b that connects with the incident end of the cylindrical surface 25, and a connection surface 93 c that is connected between the first tapered surface 93 a and the second tapered surface 93 b. An outer peripheral recess 94, into which the projection 93 fits, is formed on the outer peripheral portion of the lens element 10.

The second tapered surface 93 b is a surface having the same profile as that of the second tapered surface 26 b of the first embodiment (having the same inclination angle as that of the second tapered surface 26 b, and having the same projecting amount in the inner radial direction from the cylindrical surface 25 as that of the second tapered surface 26 b). The first tapered surface 93 a has the same inclination angle as that of the first tapered surface 26 a of the first embodiment, but has a larger projecting amount in the inner radial direction from the cylindrical surface 24 than that of the first tapered surface 26 a. The connection surface 93 c is a cylindrical surface having a constant diameter extending along the optical axis direction, and is parallel to the optical axis 10 x. The part of the projection 93 that is positioned at the innermost radial position is the connection surface 93 c. The connection surface 93 c is located at the same position in the radial direction as the maximum projecting portion 26 d of the first embodiment.

In regard to shielding peripheral light rays that pass along an outer radial side of the effective light rays EL, the projection 93 can achieve the same effect as that achieved by the projection 26 of the first embodiment. Whereas, as shown in FIG. 12 , since reflection light ray RL5′ which reflects off connection surface 93 c reaches the exit surface 12 at an incident angle that is less than the critical angle for total internal reflection, there is a possibility of ghosting occurring due to part of the light reflected from the connection surface 93 c passing through the exit surface 12 (without totally internally reflecting).

Furthermore, since the connection surface 93 c of the projection 93 is a parallel surface relative to the optical axis 10 x, a load in the optical axis direction cannot be received by the connection surface 93 c, nor can the connection surface 93 c he used as a positional reference in the optical axis direction.

Unlike the above-described comparative examples, since in the above-described first embodiment, light-distribution defects (ghosting, etc.), caused by light other than effective light rays passing through, can he prevented by the projection 26 (provided in the lens frame 20) that holds the lens element 10, superior optical performance can be achieved with a small number of components.

Furthermore, in the above-described first embodiment, by forming the inner surface of the projection 26 with the tapered surfaces 26 a, 26 b and 26 c, which are each inclined relative to the optical axis 10 x, advantageous effects can be achieved with respect to joining strength, positional precision, load bearing and air-tightness between the lens element 10 and the lens frame 20, compared to the comparative examples.

Hereinafter, a manufacturing method of the lens element 10 in the lens unit 2 of the first embodiment will be discussed. The lens element 10 is manufactured by a press-molding process using a press-molding apparatus 40 shown in FIGS. 13 through 15 . FIGS. 16 and 17 are enlarged partial views FIGS. 13 and 14 , respectively.

When the lens element 10 is manufactured in the press-molding apparatus 40, a spherical glass preform GP1, which is the material used for the lens element 10, is placed inside the lens frame 20, and the lens element 10 is integrally molded with the lens frame 20. The lens frame 20 is first finished to the final shape including the above-described projection 26 at a stage prior to placing the lens frame 20 into the press-molding apparatus 40.

The press-molding apparatus 40 is provided with an upper die 41, a lower die 42, a barrel die 43, and a barrel die 44. The “up” and “down” directions indicated in FIGS. 13 through 15 correspond to the upward and downward directions of the press-molding apparatus 40. A reference axis 40 x of the press-molding apparatus 40 is an imaginary axial line extending in the upward and downward directions (vertical direction) The central axes of the upper die 41, the lower die 42, the barrel die 43, and the barrel die 44 are aligned on the reference axis 40 x, respectively. Furthermore, the optical axis 10 x of the lens element 10 that is press-molded by the press-molding apparatus 40 is designed to be aligned with the reference axis 40 x.

The upper die 41 and the lower die 42 can be separately moved in the upward and downward directions via a raising and lowering mechanism, not shown in the drawings. The upper die 41 is movably-guided in the upward and downward directions by the barrel die 43, and the lower die 42 is movably-guided in the upward and downward directions by the barrel die 44.

The barrel die 44 is provided with a cylindrical portion 44 a positioned on the outer radial side of the lens frame 20, and a projection portion 44 b projecting radially inwardly from a lower end of the cylindrical portion 44 a. A receiving hole 44 c having a circular cross-section is formed in an inner peripheral portion of the cylindrical portion 44 a, and a guide hole 44 d having a circular cross-section is formed in an inner peripheral portion of the projection portion 44 b. The inner peripheral surfaces of both the receiving hole 44 c and the guide hole 44 d are cylindrical surfaces, respectively, having centers about the reference axis 40 x. The inner diameter of the receiving hole 44 c is greater than the inner diameter of the guide hole 44 d. The receiving hole 44 c and the guide hole 44 d constitute a single through-hole extending the in the upward and downward directions (vertical direction) with the receiving hole 44 c open at the upper end of the barrel die 44 and the guide hole 44 d open at the lower end of the barrel die 44. An annular upward-movement restriction surface (stopper flange surface) 44 e is formed at the lower end of the receiving hole 44 c on the upper face (upper surface) of the projection portion 44 b. The restriction surface 44 e is a flat surface lying orthogonal to the reference axis 40 x.

An upper end surface 44 f of the barrel die 44 is an upward-facing annular surface formed around the periphery of an upper-end opening of the receiving hole 44 c. A lower end surface 44 g of the barrel die 44 is a downward-facing annular surface formed around the periphery of a lower-end opening of the guide hole 44 d, and part of the lower end surface 44 g defines an undersurface of the projection portion 44 b. Both of the upper end surface 44 f and the lower end surface 44 g are flat surfaces lying orthogonal to the reference axis 40 x.

The barrel die 43 is a cylinder that surrounds the outer radial side of the cylindrical portion 44 a of the barrel die 44. A guide hole 43 a having a circular cross-section is formed in an inner peripheral portion of the barrel die 43 and extends through the barrel die 43 in the upward and downward directions (vertical direction). An inner surface of the guide hole 43 a is a cylindrical surface centered about the reference axis 40 x. It should be noted that the barrel die 43 and the barrel die 44 may be integrally formed (unitarily formed).

The upper die 41 is provided with a shaft portion 41 a which extends in the upward and downward directions (vertical direction), and a large-diameter portion 41 b positioned on top of the shaft portion 41 a. The shaft portion 41 a and the large-diameter portion 41 b are each cylindrical in shape, centered along the reference axis 40 x. The diameter of the large-diameter portion 41 b is larger than that of the shaft portion 41 a. A restriction surface 41 c, which is annular in shape and faces downwards, is formed at a boundary portion between the shaft portion 41 a and the large-diameter portion 41 b. The restriction surface 41 c is a flat surface that is orthogonal to the reference axis 40 x. A molding surface 41 d is formed on the end (the lower end) of the shaft portion 41 a. The molding surface 41 d is a flat surface that corresponds to the shape (profile) of the incident surface 11 of the lens element 10.

The lower die 42 is provided with a shaft portion 42 a which extends in the upward and downward directions (vertical direction), and a large-diameter portion 42 b positioned under the shaft portion 42 a. The shaft portion 42 a and the large-diameter portion 42 b are each cylindrical in shape, centered along the reference axis 40 x. The diameter of the large-diameter portion 42 b is larger than that of the shaft portion 42 a. A restriction surface 42 c, which is annular in shape and faces upwards, is formed at a boundary portion between the shaft portion 42 a and the large-diameter portion 42 b. The restriction surface 42 c is a flat surface that is orthogonal to the reference axis 40 x. A molding surface 42 d is formed on the end (the upper end) of the shaft portion 42 a. The molding surface 42 d is a concave surface that corresponds to the shape (profile) of the exit surface 12 of the lens element 10. An annular surface 42 e that corresponds to the shape (profile) of the exit peripheral rim surface 13 of the lens element 10 is formed at a peripheral portion of the molding surface 42 d.

The upper die 41 and the lower die 42 are formed from a material having superior thermal resistivity and durability so that breakage or deterioration thereof do not occur during press operations under high temperatures. Specifically, the upper die 41 and the lower die 42 may be formed from a ceramic material such as silicon carbide (SiC) or silicon nitride (Si₃N₄), or formed from a metal such as a cemented carbide. The barrel die 43 and the barrel die 44 are also formed from a material having superior thermal resistivity and durability, in the same manner as for the upper die 41 and the lower die 42.

As shown in FIGS. 13 and 16 , the lens frame 20 is arranged inside the receiving hole 44 c of the barrel die 44 with the exit end 22 of the lets frame 20 facing downward. The position of the lens frame 20 in the radial direction is determined by the inner peripheral surface of the cylindrical portion 44 a (receiving hole 44 c). The position of the lens frame 20 with respect to the upward and downward directions (vertical direction) is determined by the exit end 22 coming into contact with the restriction surface 44 e. The length of the lens frame 20 from the incident end 21 to the exit end 22 is shorter than the depth of the receiving hole 44 c (the distance from the restriction surface 44 e to the upper end surface 44 f). Therefore, with the lens frame 20 inserted into the receiving hole 44 c, the upward-facing incident end 21 is positioned lower than the upper end surface 44 f.

Due to the exit end 22 being arranged to face downward, the projection 26 within the lens frame 20 is positioned so that the second tapered surface 26 b, the third tapered surface 26 c and the first tapered surface 26 a are positioned in that order from a lower position (ordered an upward direction). Furthermore, the first tapered surface 26 a and the third tapered surface 26 c are each inclined so that the inner diameters thereof are progressively reduced in a downward vertical direction. Whereas, the second tapered surface 26 b is a tapered surface in which the inner diameter thereof is progressively larger in a downward vertical direction. In other words, the lens frame 20 is arranged in the press-molding apparatus 40 with an end of the third tapered surface 26 c of the projection 26 that has a smaller inner diameter than the other end, with respect to the optical axis direction, is positioned downward.

A spherical shaped glass preform GP1 is inserted, from above, into the through-hole 23 of the lens frame 20, which is arranged inside the press-molding apparatus 40 in the above-described manner. Alternatively, the lens frame 20 with the glass preform GP1 already inserted into the through-hole 23 may be placed into the press-molding apparatus 40. As shown in FIG. 16 , the diameter of the glass preform GP1 is smaller than the inner diameters of the cylindrical surface 24 and the cylindrical surface 25 of the lens frame 20 and is larger than the inner diameter of the projection 26. More specifically, the outer surface of the glass preform GP1 is determined to have dimensions so as to come in contact with the third tapered surface 26 c at an intermediate position with respect to the vertical direction. The center (spherical center) of the glass preform GP1 when placed on the third tapered surface 26 c is positioned on the reference axis 40 x.

When the lens frame 20 and the glass preform GP1 are being placed inside the barrel die 44, the upper die 41 is at a retreated position, further upward than the position shown in FIG. 13 . Thereafter, upon the lens frame 20 and the glass preform GP1 being placed into position, the upper die 41 is moved downward.

The upper die 41 is inserted into the guide hole 43 a of the barrel die 43 (refer to FIG. 13 ). The outer diameter of the large-diameter portion 41 b corresponds to the inner diameter of the guide hole 43 a, and the outer peripheral surface of the large-diameter portion 41 b slides along the inner peripheral surface of the guide hole 43 a to thereby guide the upward and downward movement of the upper die 41. An extremely small clearance in the radial direction is defined between the large-diameter portion 41 b and the guide hole 43 a. The position of the upper die 41 in the radial direction and the angle (the parallelism with the reference axis 40 x) are precisely determined by the barrel die 43.

Upon the upper die 41 being moved downward by a certain amount, the shaft portion 41 a enters into the through-hole 23 of the lens frame 20 from above (refer to FIGS. 13 and 16 ). The shaft portion 41 a enters into the through-hole 23 from the opening at the incident end (21) side. The outer diameter of the shaft portion 41 a corresponds to the inner diameter of the cylindrical surface 24 of the through-hole 23; however, a clearance in the radial direction between the shaft portion 41 a and the cylindrical surface 24 is slightly larger than the clearance between in the radial direction between the large-diameter portion 41 b and the guide hole 43 a. Accordingly, the upper die 41 can be moved upwardly and downwardly in the vertical direction while being guided with high precision by the guide hole 43 a of the barrel die 43 without being impeded by the lens frame 20 (the incident-side section 20A).

The lower die 42 is inserted into the guide hole 44 d of the barrel die 44 from below (refer to FIGS. 13 and 16 ). The outer diameter of the shaft portion 42 a corresponds to the inner diameter of the guide hole 44 d, and the outer peripheral surface of the shaft portion 42 a slides along the inner peripheral surface of the guide hole 44 d to thereby guide the upward and downward movement of the lower die 42. An extremely small clearance in the radial direction is defined between the shaft portion 42 a and the guide hole 44 d. The position of the lower die 42 in the radial direction and the angle (the parallelism with the reference axis 40 x) are precisely determined by the barrel die 44.

FIGS. 13 and 16 show a press-molding ready state, in which the placement of the lens frame 20 and the glass preform GP1 into the press-molding apparatus 40 is completed, and the upper die 41 and the lower die 42 are inserted into the barrel die 43 and the barrel die 44 to predetermined positions, respectively. In this state, the upper die 41 and the lower die 42 are positioned on the same vertical axis (reference axis 40 x), with the glass preform GP1 in between and facing the molding surface 41 d and the molding surface 42 d in the upward and downward directions, respectively.

A heater (not shown) is used to heat inside the press-molding apparatus 40, and is heated up to a temperature that is higher than the glass transition temperature of the glass preform GP1. Accordingly, the glass preform GP1 softens so that it, is able to be press-molded.

With the glass preform GP1 in a softened state upon being heated, the upper die 41 and the lower die 42 are moved to a close proximity of the glass preform GP1. As shown in FIGS. 14 and 17 , the lower die 42 can be inserted into the barrel die 44 to a position where the restriction surface 42 c abuts against the lower end surface 44 g, upon which further upward movement of the lower die 42 from such a position is restricted (prevented). In this state, the shaft portion 42 a of the lower die 42 enters into the through-hole 23 of the lens frame 20 from below (from the opening on the exit end (22) side). The outer diameter of the shaft portion 42 a corresponds to the inner diameter of the cylindrical surface 25 of the through-hole 23; however, the clearance in the radial direction between the shaft portion 42 a and the cylindrical surface 25 is slightly larger than the clearance in the radial direction between the shaft portion 42 a and the guide hole 44 d of the barrel die 44. Accordingly, the lower die 42 can be moved upwardly and downwardly in the vertical direction while being guided with high precision by the guide hole 44 d of the barrel die 44 without being impeded by the lens frame 20 (the exit-side section 20B).

It should be noted that when the press-molding apparatus 40 is heated, the mutual dimensions slightly change due to differences between heat expansion rates of the material of the lens frame 20 and the material of the upper and lower dies 41 and 42. However, such changes in dimensions can be absorbed by the above-described clearances between the cylindrical surfaces 24, 25 and the shaft portions 41 a, 42 a, so that the upper die 41 and the lower die 42 remain movable relative to the lens frame 20.

Upon the lower die 42 being inserted until the restriction surface 42 c comes in contact against the lower end surface 44 g of the barrel die 44, the molding surface 42 d comes in contact with the lower portion of the glass preform GP1. The position of the molding surface 42 d at such a stage is shown with a phantom line (two-dot chain line) in FIG. 16 . Since the curvature of the outer surface of the glass preform GP1 (in the state of the spherical shape shown in FIGS. 13 and 16 ) is greater than the curvature of the molding surface 42 d, which is a concave surface, the glass preform GP1 comes into point-contact with the molding surface 42 d on the reference axis 40 x.

Furthermore, the molding surface 41 d of the upper die 41 pressed onto an upper portion of the glass preform GP1 as the upper die 41 is lowered. The flat molding surface 41 d comes into point-contact with the glass preform GP1 on the reference axis 40 x. Thereafter, when the glass preform GP1, with a lower portion thereof in contact with the lower die 42, is pressed downward by the upper die 41, the glass preform GP1 is compressed in the upward and downward directions (refer to FIGS. 14 and 17 ).

Since the upper die 41 is not completely pressed downward in the state shown in FIGS. 14 and 17 , there is a partial gap between a lower portion of the glass preform GP1 and the molding surface 42 d, so that the final shapes of the exit surface 12 and the exit peripheral rim surface 13 are not yet formed.

Upon moving the upper die 41 further downward from the position shown in FIGS. 14 and 17 , the restriction surface 41 c abuts against the upper end surface 44 f of the barrel die 44 as shown in FIG. 15 ; the upper die 41 is restricted (prevented) from moving further downward from this abutment position. Hence, the upper die 41 is at a press-molded completion state with the upper die 41 fully pressed down to a press-molding completion state. At this stage, the shapes of the molding surface 41 d, the molding surface 42 d, and the annular surface 42 e are all respectively transferred onto the glass preform GP1 in the lens frame 20, to thereby form the lens element 10 provided with the incident surface 11, the exit surface 12 and the exit peripheral rim surface 13. Furthermore, the outer peripheral recess 14 is formed on the outer peripheral portion of the lens element 10 by the projection 26 of the lens frame 20.

By cooling the lens element 10 from the press-molding completion state to harden the lens element 10, a completed lens unit 2 with the lens element 10 and lens frame 20 integrated with each other is obtained. Thereupon, the upper die 41 and the lower die 42 are vertically moved away from each other in the upward and downward directions, the shaft portion 41 a is drawn upward and out of the through-hole 23, and the shaft portion 42 a is drawn downward. Thereupon, a completed lens unit 2 is removed out of the receiving hole 44 c of the barrel die 44.

In the above-described manufacturing method of the lens unit 2, since the third tapered surface 26 c of the lens frame 20, placed inside the press-molding apparatus 40, has a shape (profile) in which the inner diameter thereof progressively reduces in the downward direction, the glass preform GP1 before the press-molding operation is restricted (prevented) from moving further downward from the position at which the third tapered surface 26 c comes in contact and supports the glass preform GP1 (the position shown in FIGS. 13 and 16 ). Accordingly, even if the lower die 42, etc., does not support the glass preform GP1 from underneath, the glass preform GP1 does not drop down, and it is easy to place the glass preform GP1 inside the press-molding apparatus 40.

Furthermore, as shown in FIGS. 13 and 16 , the inclination of the third tapered surface 26 c of the lens frame 20 produces a downward pressing force on the lens frame 20 by a load acting downward on the glass preform GP1 that is placed on the third tapered surface 26 c. Specifically, the load acting downward is the downward pressing load of the upper die 41 on the glass preform GP1, and the weight of the glass preform GP1 and the upper die 41. Due to such a downward load, the lens frame 20 that is placed inside the barrel die 44 can be prevented from rising upward during a press-molding operation. If a press-molding operation were to be performed on the lens element 10 with the lens frame 20 rising upward, the positional relationship between the lens element 10 and the lens frame 20 in the optical axis direction would deviate from the designed positions, so the positional relationship between the light source 30 and the lens element 10 upon constructing the optical device 1 would be unsuitable.

When forming the lens element 10, it is necessary to place the glass preform GP1 at an appropriate position by which both the upper die 41 and the lower die 42 can correctly perform their role in the press-molding operation. For example, if a structure/configuration (unlike that of the illustrated embodiment) were to be used in which the lens frame 20 supports the glass preform GP1 at a higher (upward) position than the position shown in FIGS. 13 and 16 , when the lower die 42 is moved to the maximum upward restriction position (the position shown in FIGS. 14, 15 and 17 ), the molding surface 42 d would not be able to contact (or properly contact) the underside of the glass preform GP1. Therefore, in order to avoid such a scenario, the support position (holding position) of the glass preform GP1 by the third tapered surface 26 c is determined so that when the lower die 42 is moved up to the maximum upward restriction position, the lower portion of the glass preform GP1 comes in contact with the molding surface 42 d.

More specifically, as shown in FIG. 16 , a central position T1 for the molding surface 42 d is defined on the reference axis 40 x at the maximum upward restriction position of the lower die 42. A radius R1 (FIG. 16 ) is set to a predetermined value in accordance with a condition regarding volume, which will be discussed herein further below. Furthermore, in the case where the glass preform GP1 of radius R1 is supported at the central position T1 of molding surface 42 d, the positional relationship between the third tapered surface 26 c, the lower die 42 and the glass preform GP1 is determined so that the third tapered surface 26 c contacts the glass preform GP1 at contact positions T2 (FIG. 16 ), which are positioned further upward than the central position T1. In the illustrated embodiment, the contact positions T2 are determined so that straight lines (each indicated as radius R1 in FIG. 16 ) from each of the contact positions T2 extending toward the center of the glass preform GP1 are respectively inclined slightly upward relative to a horizontal direction. Furthermore, the third tapered surface 26 c passes through the contact positions T2 and is formed to satisfy the aforementioned conditions for total internal reflection (refer to FIG. 7 ) at the exit surface 12.

In the lens unit 2, the outer and inner lens surfaces of the lens element 10 (the incident surface 11 and the exit surface 12) are not only formed by the press-molding operation using the press-molding apparatus 40, but also the outer peripheral recess 14 of the lens element 10 that receives support from the lens frame 20 (projection 26). In other words, it is difficult to manufacture the lens element 10 by using an extra amount of glass material and remove excess glass material that has bulged outward in a radial direction, etc., upon press-molding a lens surface. Hence, it is necessary to precisely determine the volume of the glass preform GP1 so as to correspond to the volume of the press-molded lens element 10. By forming the glass preform GP1 as a sphere, the volume of the glass preform GP1 can be more easily managed. In particular, since it becomes more difficult to manage error in the amount of glass material to be used as the designed size of the lens element 10 becomes smaller, the effectiveness of using a spherical shaped glass preform GP1 becomes even more prominent.

In the press-molding completion state in which the upper die 41 and the lower die 42 are brought to the closest positions with respect to each other in the upward and downward directions (as shown in FIG. 15 ), the volume (capacity) of the space defined by the molding surface 41 d of the upper die 41, the molding surface 42 d and the annular surface 42 e of the lower die 42, and the projection 26 of the lens frame 20 determines the volume of the lens element 10 upon being press-molded. The glass preform GP1 is formed by glass material having an amount that fills (corresponds to) the capacity of the above-mentioned space.

Although the spherical shaped glass preform GP1 is superior for managing the volume of the glass material, since the glass preform GP1 can easily roll or rotate, it is necessary to make sure that the glass preform GP1 is stably supported during the press-molding process. For example, if a surface (hereinafter, a “surface from below”) that comes in contact with the glass preform GP1 from the underside were to be a convex surface, the spherical shaped glass preform GP1 could not be stably supported. Furthermore, even if the above-mentioned surface from below were to be a flat surface, since the spherical shaped glass preform GP1 may possibly roll in accordance with a load from above, it would be difficult to stably support the glass preform GP1. Accordingly, it is desirable for the above-mentioned “surface from below” to have a progressively reduced inner diameter in the downward direction (e.g., a concave surface, etc.) for the purpose of increasing stability and positional precision of the glass preform GP1, and it is desirable for the inclination of the “surface from below” to be large (a large curvature in the case of a concave surface) with respect to the reference axis 40 x.

As shown in FIG. 16 , the third tapered surface 26 c which contacts the glass preform GP1 in the lens frame 20 satisfies the above-mentioned conditions for the “surface from below”. In particular, since the third tapered surface 26 c has a conical shape having a central axis along the reference axis 40 x, the position of the glass preform GP1 can be determined both in the optical axis direction and the radial direction by its own weight at a stage before the press-molding operation, so that the glass preform GP1 can be stably supported with high precision. Furthermore, when a pressing load is applied from the upper die 41 onto the glass preform GP1, due to the lens frame 20 being downwardly pushed via the third tapered surface 26 c, the lens frame 20 can be prevented from rising upward and a high-precision press-molding operation can be achieved.

Furthermore, the molding surface 42 d of the lower die 42 which is positioned below the glass preform GP1 is a concave surface corresponding to the convex shaped exit surface 12 of the lens element 10, and satisfies the above-mentioned conditions for the “surface from below”. Whereas, the molding surface 41 d of the upper die 41 that is positioned above the glass preform GP1 is a flat surface corresponding to the flat incident surface 11 of the lens element 10. When the upper die 41 and the lower die 42 are brought towards each other to press-mold the lens element 10 from the glass preform GP1, by positioning the concave molding surface 42 d at the bottom instead of the flat molding surface 41 d, a stabilizing action against the glass preform GP1 in the optical axis direction and the radial direction can be obtained in accordance with the load in the downward direction.

In other words, out of the incident surface 11 and the exit surface 12 of the positive powered lens element 10, by forming (setting) the molding surface (the molding surface 42 d in the illustrated embodiment) that molds the convex lens surface (the exit surface 12 in the illustrated embodiment) that has a large curvature (small curvature radius) on the lower die 42 and press-molding the lens element 10 therewith, positional deviation of the glass preform GP1 can be suppressed and the molding precision can be improved.

Furthermore, by arranging the lens frame 20 in the press-molding apparatus 40 so that the smaller end of the inner diameter of the third tapered surface 26 c faces downward, and placing the glass preform GP1 onto the third tapered surface 26 c, the glass preform GP1 can be stably supported from before the press-molding operation and throughout the entire press-molding operation itself.

Furthermore, the first tapered surface 26 a and the third tapered surface 26 c of the lens frame 20, which is arranged within the press-molding apparatus 40 so that the smaller inner diameter side thereof faces downward, each have a function of appropriately controlling the deforming of the glass preform GP1 during the press-molding operation.

As shown in FIGS. 16 and 17 , from the initial stage of the press-molding operation until the final stage thereof, the position of the glass preform GP1 which directly receives the pressing force from the upper die 41 is a contact position on the reference axis 40 x. However, a compression load also occurs on a peripheral portion of the glass preform GP1, far from the reference axis 40 x in the radial direction, due to the downward pressing force also being received by the first tapered surface 26 a and the third tapered surface 26 c. Accordingly, a suitable surface pressure can be obtained during the press-molding operation so that the peripheral edge portion of the lens element 10 including the outer peripheral recess 14 can be formed with high precision. Furthermore, the softened glass preform GP1 can reliably enter around and into the lower portion of the projection 26 by following the first tapered surface 26 a and the third tapered surface 26 c, which constitute a two-stage inclination, and along the second tapered surface 26 b that inclines in the opposite direction thereto. Accordingly, due to the projection 26 of the lens frame 20, a press-molding operation can be efficiently performed while suppressing any inclination or decentration of the glass preform GP1 with respect to the reference axis 40 x.

Hence, by using the press-molding apparatus 40, the lens element 10 can be efficiently molded with high precision, and production yield of the lens unit 2 can be improved.

A second embodiment of the lens unit 2 is shown in FIG. 18 . In the lens unit 2 of the above-described first embodiment, the inner surface of the incident-side section 20A of the lens frame 20 is a smooth cylindrical surface (24) having a uniform profile (constant diameter) along the optical axis direction. Whereas, the lens unit 2 according to the second embodiment differs with respect to further measures taken against reflection light on the inner surface of the incident-side section 20A. The lens unit 2 according to the second embodiment has the same structure as that of the first embodiment except for the inner surface of the incident-side section 20A.

As shown in FIG. 18 , the inner surface of the incident-side section 20A of the second embodiment is provided with a composite inner surface (reflection control portion) 27 formed of a plurality of surface portions of differing inner diameters and inclinations. The composite inner surface 27 is provided with a first cylindrical surface 27 a, a first tapered surface 27 b, a second tapered surface 27 c, and a second cylindrical surface 27 d, in that order from the incident side.

The second cylindrical surface 27 d is a cylindrical surface having substantially the same diameter as that of the cylindrical surface 24 of the first embodiment. The first cylindrical surface 27 a is a cylindrical surface having a smaller inner diameter than that of the second cylindrical surface 27 d. The first tapered surface 27 b has a conical shape (is a partial conical surface) having an inner diameter that is smallest at a boundary with the first cylindrical surface 27 a and the inner diameter is progressively larger toward the second tapered surface 27 c (exit side) with respect to the optical axis direction. The second tapered surface 27 c has a conical shape s a partial conical surface) having an inner diameter that is largest at a boundary with the first tapered surface 27 b, and the inner diameter is progressively smaller toward the second cylindrical surface 27 d (exit side) with respect to the optical axis direction.

Reflection light rays RL3 and RL4 emitted from the light source 30 and reflected off the first tapered surface 27 b are shown in FIG. 18 . The reflection light ray RL3 is shown as a light ray that is reflected by the first tapered surface 27 b at a position near the first cylindrical surface 27 a (incident side), and the reflection light ray RL4 is shown as a light ray that is reflected by the first tapered surface 27 b at a position near the second tapered surface 27 c (exit side). Since the first tapered surface 27 b reflects the reflection light ray RL3 so as to travel toward the projection 26, the reflection light ray RL3 is obstructed from traveling toward the exit side by the projection 26. The reflection light ray RL4 is obstructed from traveling toward the exit side by the second tapered surface 27 c, which is adjacent to the first tapered surface 27 b.

Accordingly, in the lens frame 20 of the second embodiment, since light rays reflected off the inner surface of the incident-side section 20A can be prevented from exiting through the lens element 10, an even more superior optical performance (ghosting prevention effect) can be achieved. It should be noted that suppression of the light rays from the inner surface of the incident-side section 20A is not limited to the structure shown in FIG. 18 . For example, it is also possible to use a light-shielding line structure having repetitive fine concavities and convexities with respect to the optical axis direction.

A lens unit 2 and a manufacturing method (manufacturing apparatus) thereof according to a third embodiment is shown in FIGS. 19 through 21 . The lens unit 2 according to the third embodiment uses a biconvex lens element 50 having a positive refractive power. In other words, the lens element 50 is provided with an incident surface 51, which is a convex surface convexing toward (protruding toward) the incident side, and an exit surface 52, which is a convex surface convexing toward (protruding toward) the exit side. The incident surface 51 has a larger curvature than that of the exit surface 52. An incident peripheral rim surface 53 is formed at a peripheral annular region of the incident surface 51. The incident peripheral rim surface 53 is approximately perpendicular (orthogonal) to an optical axis 50 x of the lens element 50.

A projection 28 is formed inside the intermediate section 20C of the lens frame 20 instead of the projection 26 of the first embodiment. The projection 28 is continuously provided over the entire circumferential direction of the lens frame 20. The projection 28 has a shape (profile) which is reversed in the optical axis direction compared to that of the projection 26 of the first embodiment. Specifically, the projection 28 is provided with a first tapered surface 28 a that connects with the exit end of the cylindrical surface 24, a second tapered surface 28 b that connects with the incident end of the cylindrical surface 25, and a third tapered surface 28 c connected between the first tapered surface 28 a and the second tapered surface 28 b.

The first tapered surface 28 a has a progressively reduced inner diameter from the cylindrical surface 24 (the incident side) toward the exit side. The second tapered surface 28 b has a progressively reduced inner diameter from the cylindrical surface 25 (exit side) toward the incident side. The third tapered surface 28 c has a progressively reduced inner diameter from the second tapered surface 28 b (exit side) toward the first tapered surface 28 a (incident side).

In other words, the inclination direction of the third tapered surface 28 c relative to the optical axis 50 x of the lens element 50 is the opposite to that of the inclination direction of the third tapered surface 26 c relative to the optical axis 10 x in the first embodiment. Furthermore, reflection light rays that reflect off the third tapered surface 28 c and travel toward the exit surface 52 not totally reflecting (total internal reflection does not occur) is also different from the first embodiment.

An outer peripheral portion of the lens element 50 is provided with an outer peripheral recess 54 that corresponds to the shape (profile) of the projection 28. The lens element 50 is fixed within the lens frame 20 with the projection 28 fixedly fitted into the outer peripheral recess 54.

In the same manner with the projection 26 of the first embodiment, the projection 28 has a function by which harmful light such as peripheral light that passes radially outside the effective light rays can be shielded (prevented from passing through the exit surface 52) while allowing (not shielding) the effective light rays passing within the effective aperture of the incident surface 51 and exiting within the effective aperture of the exit surface 52. Furthermore, due to the three tapered surfaces 28 a, 28 b and 28 c of the projection 28 supporting the lens element 50, the joining strength, positional precision, load bearing and air-tightness, etc., between the lens element 50 and the lens frame 20 can be improved.

A press-molding apparatus 60 for press-molding the lens element. 50 of the third embodiment is shown in FIGS. 20 and 21 . Although the dimensions in the optical axis direction differ, the fundamental structures of an upper die 61, a lower die 62, a barrel die 63 and a barrel die 64 of the press-molding apparatus 60 are in common with the above-described upper die 41, the lower die 42, the barrel die 43 and the barrel die 44 of the press-molding apparatus 40, respectively. Accordingly, each component/part of the press-molding apparatus 60 that functions in a similar manner to that of the press-molding apparatus 40 is indicated in FIGS. 20 and 21 with an addition “1” added to the left side of the numerals corresponding to the those of the press-molding apparatus 40, and duplicate descriptions thereof have been omitted.

Similar to when the lens element 10 is press-molded in the first embodiment, when the lens element 50 is press-molded, the press-molding apparatus 60 is set so that a molding surface for forming a lens surface having a large convex curvature (a small radius of curvature) is provided on the lower die 62. In regard to the shape (profile) of the lens element 50, which is a biconvex lens element, since the incident surface 51 is a convex surface having a larger curvature than that of the exit surface 52, a molding surface 66 which forms incident surface 51 is provided on the lower die 62. Furthermore, a molding surface 65 which forms the exit surface 52, which is a convex surface having a smaller curvature than that of the incident surface 51, is provided on the upper die 61. Hence, in accordance with the difference in curvatures between the incident surface 51 and the exit surface 52, the molding surface 66 of the lower die 62 is concave surface having a larger curvature than that of the molding surface 65 of the upper die 61.

The orientation of the lens frame 20 when placed in the press-molding apparatus 60 is vertically opposite to the orientation of the lens frame 20 in the first embodiment. Namely, the incident end 21 is faced downward when the lens frame 20 is inserted into a receiving hole 144 c of the barrel die 64. Thereafter, the incident end 21 come in contact with a restriction surface 144 e of the barrel die 64, thereby determining the position of the lens frame 20 in the upward/downward direction.

With the lens frame 20 inserted into the receiving hole 144 c, the upward-facing exit end 22 is positioned downward relative to the upper end surface 144 f (below the upper end surface 144 f). Furthermore, the inclination directions and angles, relative to the reference axis 60 x of the press-molding apparatus 60, of the first tapered surface 28 a, the second tapered surface 28 b, and the third tapered surface 28 c of the projection 28 are substantially the same as the inclination directions and angles of the second tapered surface 26 b, the first tapered surface 26 a, and the third tapered surface 26 c of the projection 26, respectively, of the first embodiment shown in FIGS. 13 through 17 .

Hence, a spherical shaped glass preform GP2 is inserted into the through-hole 23 of the lens frame 20, which is placed in the press-molding apparatus 60, from above (from the exit end (22) side). Alternatively, the lens frame 20 may be placed inside the press-molding apparatus 60 with the lens frame 20 already having the glass preform GP2 inserted into the through-hole 23 thereof. As shown in FIG. 20 , the glass preform GP2 is placed on (rests on) the third tapered surface 28 c of the projection 28 inside the lens frame 20. The third tapered surface 28 c, the inner diameter thereof progressively reducing in a downward direction, can stably hold the glass preform GP2 with high precision. Furthermore, the press load of the upper die 61 against the glass preform GP2 and the weight of the glass preform GP2 itself are able to prevent the lens frame 20 from rising in the barrel die 64.

The upper die 61, which is movably-guided in the upward and downward directions via the barrel die 63, is provided with a molding surface 65 on the end (lower end) of a shaft portion 141 a. As described above, the molding surface 65 is a concave surface having a shape corresponding to the exit surface 52 of the lens element 50.

The lower die 62, which is movably-guided in the upward and downward directions via the barrel die 64, is provided with the molding surface 66 on the end (upper end) of a shaft portion 142 a. As described above, the molding surface 66 is a concave surface having a shape corresponding to the incident surface 51 of the lens element 50. Furthermore, an annular surface 67, having a shape corresponding to the incident peripheral rim surface 53 of the lens element 50, is formed around the periphery of the molding surface 66.

The glass preform GP2 is heated and softened inside the press-molding apparatus 60. From the press-molding ready state shown in FIG. 20 , the upper die 61 and the lower die 62 are moved to close in the upward and downward directions The shaft portion 142 a of the lower die 62 moves upward into the through-hole 23 of the lens frame 20, and the molding surface 66 abuts against the lower portion of the glass preform GP2. The shaft portion 141 a of the upper die 61 moves downward into the through-hole 23 of the lens frame 20, and the molding surface 65 comes in contact against the upper portion of the glass preform GP2. Thereafter, the glass preform GP2, sandwiched in between the molding surface 65 and the molding surface 66, is pressed and deformed in accordance with the shapes of the molding surface 65 and the molding surface 66.

Since the molding surface 66, which is a concave surface having a larger curvature than that of the molding surface 65, is at a lower position, when the glass preform GP2 is pressed downwards in the press-molding operation, the precision of the molding can be improved by suppressing positional deviation of the glass preform GP2.

The upper die 61 and the lower die 62 approach each other until a restriction surface 142 c comes in contact with a lower end surface 144 g of the barrel die 64 and is restricted from movement thereby, and a restriction surface 141 c comes in contact with the upper end surface 144 f of the barrel die 64, to thereby reach the press-molding completion state shown in FIG. 21 to obtain a press-molded lens element 50.

A lens unit 2 and a manufacturing method (manufacturing apparatus) thereof according to a fourth embodiment is shown in FIGS. 22 through 24 . The lens unit 2 according to the fourth embodiment uses a biconvex lens element 70 having a positive refractive power. The difference with the lens element 70 compared to the lens element 50 of the third embodiment is that an exit surface 72, which has a convex surface convexing toward the exit side, has a larger curvature (a smaller radius of curvature) than an incident surface 71, which has a convex surface convexing toward the incident side. An exit peripheral rim surface 73 is formed at a peripheral annular region of the exit surface 72. The exit peripheral rim surface 73 is approximately perpendicular (orthogonal) to the optical axis 70 x of the lens element 70.

The structure of the lens frame 20 is the same as that of the third embodiment, and is likewise provided with a projection 28 formed on the inner side of the intermediate section 20C. The projection 28 is fixedly fitted into an outer peripheral recess 74 of the lens element 70 so that the lens element 70 is fixed within the lens frame 20.

A press-molding apparatus 80 for press-molding the lens element 70 of the fourth embodiment is shown in FIGS. 23 and 24 . The press-molding apparatus 80 has a structure that is substantially the same as the press-molding apparatus 60 of the third embodiment. Components in the fourth embodiment that are in common with those of the third embodiment are indicated with the same numeral designators, and duplicate descriptions thereof have been omitted.

The press-molding apparatus 80 is provided with a molding surface 84 on a lower die 82 for molding the incident surface 71 of the lens element 70, and is provided with a molding surface 83 on an upper die 81 for molding the exit surface 72. Furthermore, an annular surface 85 is formed on the upper die 81 for forming the exit peripheral rim surface 73 on the lens element 70. In other words, the fourth embodiment differs from the press-molding apparatus 40 of the first embodiment and the press-molding apparatus 60 of the third embodiment by having a configuration in which instead of providing the molding surface 83 that forms the exit surface 72 (which has a large convex curvature) on the lower die 82, the molding surface 84 that forms the incident surface 71 (which has a small convex curvature) is provided on the lower die 82.

As shown in FIG. 23 , the lens frame 20 is inserted into the receiving hole 144 c of the barrel die 64 of the press-molding apparatus 80 with the incident end 21 of the lens frame 20 facing downward. Accordingly, the third tapered surface 28 c of the projection 28 is oriented so that the smaller inner diameter thereof is positioned downward (so that the end of the third tapered surface 28 c that has a smaller inner diameter than the other end, with respect to the optical axis direction, is positioned downward). Furthermore, a spherical shaped glass preform GP3 is placed on the third tapered surface 28 c. The third tapered surface 2 c, the inner diameter thereof progressively reducing in a downward direction, can stably hold the glass preform GP3 with high precision. Furthermore, the press load of the upper die 81 against the glass preform GP3 and the weight of the glass preform GP3 itself are able to prevent the lens frame 20 from rising in the barrel die 64.

The glass preform GP3 is heated and softened inside the press-molding apparatus 80. From the press-molding ready state shown in FIG. 23 , the upper die 81 and the lower die 82 are moved to close in the upward and downward directions. The molding surface 84 of the lower die 82 comes in contact against the lower portion of the glass preform GP3, and the molding surface 83 of the upper die 81 comes in contact against the upper portion of the glass preform GP3. Thereafter, the glass preform GP3, sandwiched in between the molding surface 83 and the molding surface 84, is pressed and deformed in accordance with the shapes of the molding surface 83 and the molding surface 84.

The lower molding surface that is positioned underneath the glass preform GP3 during a press-molding operation is the molding surface 84 which is a concave surface having a smaller curvature than that of the molding surface 83. However, it should be noted that since the molding surface 84 is a concave surface, a certain effect of stabilizing the glass preform GP3 can be obtained compared to the case where the lower molding surface is a convex surface or a flat surface.

The upper die 81 and the lower die 82 approach each other until a restriction surface 142 c comes in contact with a lower end surface 144 g of the barrel die 64 and is thereby restricted from further movement, and a restriction surface 141 c comes in contact with the upper end surface 144 f of the barrel die 64, to thereby reach the press-molding completion state shown in FIG. 24 to obtain a press-molded lens element 70.

As described above, each lens unit 2 according to each illustrated embodiment can exhibit improvements in positional precision, joining strength, load bearing and air-tightness between the lens frame 20 and the lens element 10, the lens element 50 or lens element 70. Furthermore, an improvement in optical performance can be achieved by preventing harmful light rays using the simple structure of the projection 26 or the projection 28 of the lens frame 20.

Furthermore, by using the third tapered surface 26 c (or 28 c) provided on the projection 26 (or 28) of the lens frame 20, the support precision between he lens frame 20 and the glass preform GP1 (or GP2 or GP3) during the press-molding operation in the press-molding apparatus 40 (or 60 or 80) can be increased and the productivity can be improved.

As described above in regard to the press-molding apparatus 40 and the press-molding apparatus 60, a further improvement in productivity can be achieved by forming the molding surface on the lower die with a concave surface having a larger curvature compared to that of the molding surface formed on the upper die.

However, the present invention is not limited to the above-described embodiments of this disclosure, various modification may be made without departing from the scope of the present invention.

Although in the above-described embodiments the lens element (10, 50 or 70) provided in the lens unit 2 is either a plano-convex lens element or a biconvex lens element, the lens profile of the lens element is not limited thereto. For example, the present invention may also be applied to a meniscus lens element having a positive refractive power. In such a case, it is desirable to provide the molding surface for forming the convex surface of the meniscus lens element in the lower die of the press-molding apparatus.

The projection 26 (28) in the lens frame 20 of the above-illustrated embodiments is provided continuously around the entire circumference of the lens frame 20 centered about the optical axis 10 x (50 x, 70 x) of the lens element 10 (50, 70). Such a structure is advantageous for achieving strength, light-shielding ability and air-tightness. However, the projection of the lens frame may be alternatively provided with partial (discontinuous) projections in the circumferential direction about the optical axis instead of the entire inner circumference of the lens frame 20.

The projection 26 (28) of the lens frame 20 in the above-described embodiments is provided with three tapered surfaces at different positions with respect the optical axis direction. Namely, the intermediate portion (with respect the optical axis direction) of the 26 (28) is provided with only the third tapered surface 26 c (28 c) having a constant inclination. Such a structure is simple, facilitates the manufacture of the lens frame 20, and is also advantageous for attaining higher precision. However, it is also possible to provide two or more tapered surfaces in the intermediate portion (a portion that corresponds to the third tapered surface 26 c (28 c)) of the projection of the lens frame; these two tapered surfaces, having different inclination angles and inclination directions, being continuously formed with respect to the optical axis direction. In other words, the projection of the lens frame of the present invention may be provided with not less than four tapered surfaces along the optical axis direction.

Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention. 

What is claimed is:
 1. A method for manufacturing a lens unit comprising: a lens element provided with a convex surface on at least one of an incident surface and an exit surface of the lens element, the lens element having a positive refractive power that condenses light rays, emitting from a light source, at a predetermined position; and a lens frame that supports the lens element within the lens frame, the lens frame provided with a projection that projects in an inner radial direction from an inner portion of the lens frame, wherein the lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element, wherein the projection is provided, on an inner peripheral portion thereof, with a first surface positioned on an incident side in an optical axis direction of the lens element, a second surface positioned on an exit side in the optical axis direction, and a third surface positioned between the first surface and the second surface, and wherein the first, second and third surfaces are tapered surfaces that are respectively inclined relative to the optical axis direction, wherein the method comprising: placing the lens frame into a press-molding apparatus with the lens frame oriented so that an end of the third surface that has a smaller inner diameter than the other end, with respect to the optical axis direction, is positioned downward; placing a glass preform onto the third surface; and press-molding the glass preform using an upper die and a lower die of the press-molding apparatus to form the lens element.
 2. The method for manufacturing the lens unit according to claim 1, wherein a molding surface for molding one surface having a largest convex curvature out of the incident surface and the exit surface of the lens element is formed on the lower die, and a molding surface for molding the other surface of the incident surface and the exit surface of the lens element is formed on the upper die.
 3. The method for manufacturing the lens unit according to claim 2, wherein the glass preform is formed into a spherical shape, wherein the molding surface of the lower die comprises a concave surface, and wherein a curvature of an outer surface of the glass preform is larger than a curvature of the molding surface of the lower die.
 4. The method for manufacturing the lens unit according to claim 3, wherein the inner diameter of the end of the third surface that has a smaller inner diameter than the other end is smaller than the diameter of the glass preform; and wherein the glass preform, before the press-molding operation, is restricted from moving downward from the position at which the glass preform comes into contact with the third surface and is supported thereby.
 5. The method for manufacturing the lens unit according to claim 1, further comprising: placing the lens frame, the glass preform, the upper die and the lower die into the press-molding apparatus; heating the inside of the press-molding apparatus and softening the preform; and pressing the glass preform by moving the upper die and the lower die to a close proximity of the glass preform.
 6. The method for manufacturing the lens unit according to claim 5, wherein the lower die is configured to be movable, in the upward and downward directions, with respect to the lens frame, wherein the press-molding apparatus is provided with a maximum upward restriction position of the lower die in the upward and downward directions, with respect to the lens frame, wherein the support position, of the glass preform, defined by the third surface is determined so that the molding surface of the lower die comes into contact with the lower portion of the glass preform when the lower die moves to the maximum upward restriction position.
 7. The method for manufacturing the lens unit according to claim 1, wherein the inclination of the third surface of the lens frame is configured to generate a downward pressing force on the lens frame by a load acting downward on the glass preform that is placed on the third surface.
 8. The method for manufacturing the lens unit according to claim 1, wherein the press-molding apparatus is provided with a barrel die which guides the lower die to be movable in the upward and downward directions, wherein the barrel die is provided with a projection portion projecting radially inwardly from the inner peripheral surface of a receiving hole, and wherein the lens frame is arranged inside the receiving hole of the barrel die so that the position of the lens frame with respect to the upward and downward directions is determined by a lower end of the lens frame coming into contact with the projection portion.
 9. The method for manufacturing the lens unit according to claim 3, wherein the molding surface comprises a concave surface, on which the glass preform point-contacts.
 10. The method for manufacturing the lens unit according to claim 1, wherein the inner diameter of the other end of the third surface progressively reduces, in the downward direction, to the inner diameter of the end of the third surface.
 11. The method for manufacturing the lens unit according to claim 5, wherein the upper die, the lower die and the lens frame are formed to have clearances therebetween in a radial direction to absorb dimensional changes due to differences of heat expansion rates of the upper die, the lower die and the lens frame.
 12. The method for manufacturing the lens unit according to claim 7, wherein the load acting downward on the glass preform is made by a downward pressing load of the upper die, a weight of the glass preform and that of the upper die.
 13. A method for manufacturing a lens unit comprising: a lens element provided with a convex surface on at least one of an incident surface and an exit surface of the lens element, the lens element having a positive refractive power that condenses light rays, emitting from a light source, at a predetermined position; and a lens frame that supports the lens element within the lens frame, the lens frame provided with a projection that projects in an inner radial direction from an inner portion of the lens frame, wherein the lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element, wherein the projection is provided, on an inner peripheral portion thereof, with a tapered surface that is inclined relative to the optical axis direction wherein the method comprising: placing the lens frame, into a press-molding apparatus, in a manner that an end of the tapered surface of the projection having a smaller inner-diameter is oriented downward; placing a glass preform onto the tapered surface, thereby the glass preform is restricted from moving downward; and press-molding the glass preform using an upper die and a lower die of the press-molding apparatus to form the lens element.
 14. The method for manufacturing the lens unit according to claim 13, wherein the glass preform is formed into a spherical shape, wherein the molding surface of the lower die comprises a concave surface, and wherein a curvature of an outer surface of the glass preform is larger than a curvature of the molding surface of the lower die.
 15. The method for manufacturing the lens unit according to claim 13, further comprising: placing the lens frame, the glass preform, the upper die and the lower die into the press-molding apparatus; heating the inside of the press-molding apparatus and softening the preform; and pressing the glass preform by moving the upper die and the lower die to a close proximity of the glass preform.
 16. The method for manufacturing the lens unit according to claim 15, wherein the lower die is configured to be movable, in the upward and downward directions, with respect to the lens frame, wherein the press-molding apparatus is provided with a maximum upward restriction position of the lower die in the upward and downward directions, with respect to the lens frame, wherein the support position, of the glass preform, defined by the tapered surface is determined so that the molding surface of the lower die comes into contact with the lower portion of the glass preform when the lower die moves to the maximum upward restriction position. 